my daughter has a 2003 chevy cavalier, and it is making a popping noise under the hood somewhere, when you drive it up to about 15MPH it starts making the popping sound,

First thing you should do when haveing strange noises is to determin exactly where your noise is comeing from, lift front end (with jack stands)have someone control speed of rotation as you inspect front end (carefully), find noise if you dont hear noise at 15 mp + then check tires , if noise only persists when the strain of pulling the weight of car is applied then check engine (may not be recieve'ing proper amount of gas or out of timeing ),,,,,Once you find your noise you can fix it,,,remember to always buy a (I like haynes)manual for your car .

Sounds like the CV axle joints might be bad but you replaced those. Check your struts and the hardware that connects them to the knuckle? Bearings? How about the control arm bushings? Motor mounts? Flex pipe in the exhaust shot? how is it running? Converter? See a professional for a proper diagnosis. Might be cheaper than continually throwing parts at it